The Analytical Approach Edited by Jeanette G. Grasselli

Papyrus The Paper of Ancient Egypt

Papyrus Ebers (16th century B.C.) contains, in more than 100 columns, about 10 000 medical recipes for treatment of all kinds of diseases

Egypt was not only the kingdom of the pharaohs with their pyramids, temples, tombs, mummies, and a mul­tiform world of gods, but also the land of officials, scribes, and the written word (1). The importance of the latter is evident from the texts and inscrip­tions on papyrus, the "paper" of an­cient Egypt. These papyri contained texts referring to the public and pri­vate life in ancient Egypt; they are the written heritage of a culture that ex­isted over thousands of years. The old­est papyrus ever found originates from the First Dynasty (3000 B.C.); the ear­liest inscribed papyrus is assigned to the Fifth Dynasty (2400 B.C.).

At the beginning of the 20th centu­ry, scientific excavation campaigns by archeologists in middle and upper Egypt uncovered an unexpected, rich cache of papyri writings, excellent­ly preserved due to the dry Egyptian climate and overlying desert sand. These papyri are now located in Egyp­tian collections in European museums, and their availability for scientific ex­amination allows us to learn much about the age, composition, and pro­cessing of this ancient paper. To ex­amine these materials we selected a number of different analytical tech­niques: thermoanalytical methods— thermogravimetric analysis (TG), dif­ferential thermal analysis (DTA), and thermal mechanical analysis (TMA); mass spectrometry (MS); and optical and electron microscopy. These tech­niques required only small amounts of the original ancient samples, yet pro­vided much useful information. Before we began our investigation, however, we had to study the papyrus plant it­self.

Cyprus Papyrus

Papyrus was grown in various parts of the Near East and Egypt, including the delta of the Nile. The stems, which are used to make the writing material, have a triangular cross section and may reach a height of 3-6 m. Table I shows the complete elemental analysis of both ancient (1300 B.C.) and fresh (1977) papyri.

The main components of the papy­rus plant, cellulose, hemicellulose, and lignin, are shown in the photomicro­graph of a section of fresh papyrus

1220 A · ANALYTICAL CHEMISTRY, VOL. 55, NO. 12, OCTOBER 1983 0003-2700/83/A351-1220$01.50/0 © 1983 American Chemical Society

H. G. Wiedemann Mettler Instrumente AG CH-8606 Greifensee/Zurich Switzerland

G. Bayer Institute of Crystallography and Petrography Swiss Federal Institute of Technology (ΕΤΗ) 8092 Zurich Switzerland

Damaged painting in an ancient papyrus (Book of Death). The barge was originally painted with green copper acetate

stem and in the DTA curves of sam­ples from different regions of the stem (Figure 1). The upper curve (a) is from a collateral bundle, which contains more "incrust" (lignin) than cellulose. The middle curve (b) corresponds to the cellulose region that surrounds the collateral bundle. Cellulose and hemi-cellulose predominate; and the shoul­der on the lignin peak indicates the presence of both monomeric and di-meric phenols. The material of the third sample was taken from the inter­mediate layer between the collateral bundle and the cellulose region. Its lower curve (c) shows more cellulose and hemicellulose than monomeric phenols of lignin.

How Was Papyrus Made? Looking through the many exam­

ples of original literature and pictures

ANALYTICAL CHEMISTRY, VOL. 55, NO. 12, OCTOBER 1983 · 1221 A

from ancient Egypt, one finds descrip­tions of all kinds of technical pro­cesses and recipes for a variety of products. However, even though papy­rus was used in large quantities, the details of its original manufacturing process are missing. Since papyrus was rather expensive, perhaps the pro­cess was kept secret to preserve a mo­nopoly for its production and export.

The only picture that gives some in­formation, at least of the first steps during the fabrication of papyrus, was a mural discovered in the tomb of Puy-em-Re. It shows the harvesting of papyrus, plus the bundling and de­barking of the stems. A detailed de­scription of the subsequent produc­tion of "papyrus paper" may be found, however, in Pliny's "Natural History" (80 A.D.) in which he also refers to pos­sible manufacturing processes in an­

cient Egypt (2). The following is taken from a recent English translation by H. Rackham of the fourth volume of

Table I. Elemental Analysis of Papyrus

Ancient Fresh sample papyrus (% by (% by

Elements weight) weight)

Oxygen 38.56 52.70 Carbon 36.22 40.27 Hydrogen 4.78 4.37 Nitrogen 1.55 0.95 Sulfur 0.55 0.40 Silicon 7.17 0.54 Iron 1.75 trace Aluminum 4.05 0.009 Calcium 2.64 0.14 Magnesium 0.83 0.07 Sodium 1.43 0.43

Magnification 40x

Monomeric Lignin

Polymeric Lignin

Hemicellulose

Cellulose

Exotherm

0.5 mW

Figure 1. Photomicrograph (40x) of a section of fresh papyrus stem and different regions of the stem. DTA curves in oxidizing atmosphere of (a) collateral bundle; (b) cellulose region surrounding collateral bundle; (c) intermediate layer

Table II. Composition (Wt % ) of Ancient Papyri Determined from TG Measurements

Sample Ash weight Water Cellulose Lignin content

Papyrus (me) (%> (%) <%) <%) 1900 B.C. 1.045 4.93 54.81 32.77 7.49 344 B.C. 1.285 6.77 58.14 27.83 7.26

5 B.C. 2.368 7.47 62.04 22.42 8.07 578 A.D. 2.430 7.12 53.29 24.81 14.78

Sicily, 1977 A.D. 3.157 4.85 53.12 28.86 13.21 Egypt, 1977 A.D. 1.424 4.92 68.96 24.02 2.04

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this encyclopedia (3): "The process of making paper from papyrus is to split it with a needle into very thin strips made as broad as possible, the best quality being in the center of the plant, and so on in the order of its splitting up. Paper of all kinds is 'woven' on a board moistened with water from the Nile, muddy liquid supplying the effect of glue. First an upright layer is smeared onto the table, using the full length of papyrus available after the trimmings have been cut off at both ends, and after­wards cross strips complete the lat­ticework. The next step is to press it in presses, and the sheets are dried in the sun and then joined together. There are never more than twenty sheets to a roll." This description is historically very valuable but the accuracy of Pliny's statement about the gluing ac­tion of the muddy Nile water is ques­tionable (especially since we discov­ered that filtered Nile water produces the same effect).

According to research by Hepper and Reynolds (4), it is likely that the adhesion between the individual pa­pyrus strips is provided by the gum­like substances from the cell sap of the pith of papyrus. These are identified as water-soluble polymers of galac­tose, arabinose, and a trace of rham-nose—constituents that are also found in other vegetable gums. However, other investigations by Ragab (5) con­cluded that the adhesion between the papyrus strips has more of a physical than a chemical nature. According to Ragab the physical pressing together of the crosswise-laid sheets causes the parenchymatous tissues to dovetail and merge. This becomes permanent during the drying and shrinking of the strips, thus ensuring good adherence.

From his own investigations Ragab further concluded that starch was not used as a gluing substance in ancient Egypt. However, our microscopic in­vestigations proved that starch was definitely used in ancient Egyptian papyri at least until 300 B.C. Microsco­py of over 50 microtome cuts from various ancient papyri showed that they all contained a layer of starch ad­hesive between the papyrus layers. Figure 2 shows both a recent papyrus (1976) and an ancient papyrus (344 B.C.), and the presence of starch in the latter is very evident. Our own thoughts are that perhaps the use of starch was discontinued because of the loss of the knowledge of the pro­cess or the lack of starch due to a bad corn harvest.

Thermoanalytical Investigations

Typical TG and DTG curves of a papyrus sheet are shown in Figure 3. The oxidative degradation of cellulose occurs at about 250-350 °C followed

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by that of lignin at 380-450 °C (6). Heating in an inert atmosphere (nitro­gen or argon) produced a very un­characteristic DTG curve. Only the combustion in air allowed differentia­tion between various kinds of papyri based on the position, shape, and height of the bands.

The position and the height of the lignin peak especially are very sensi­tive to the processing of the papyrus, to its age, and to its state of preserva­tion (7). Table II shows the composi­tion of several different papyri, in­cluding two recent samples from Sicily and Egypt (8), in terms of their H 2 0 , cellulose, and lignin content as de­rived from TG/DTG measurements.

The Sicilian and Egyptian material showed distinctly different behavior during the decomposition process. Corresponding DTA curves (Figure 4) show that the lignin peak of the Egyp­tian material is much smaller than that of the Sicilian material. These two curves represent the two basic types of DTA curves that were ob­served for most of the ancient papyri.

To determine if differences in these curves could be caused by different treatments, we produced papyrus sheets with two different pretreat-ments—pressing and beating. Figure 5 shows the effect of the pretreatment on the shape of the peaks. The differ­ence between the lignin peaks of the pressed (Figure 5a) and of the beaten (Figure 5b) papyri is caused by me­chanical destruction of the material,

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Figure 3. Typical (a) TG and (b) DTG curves of an ancient (1900 B.C.) papyrus sheet (heating rate: 6 °C/min)

Figure 2. Photomicrographs of (a) microtomed papyrus sheet (1976) with no adhesive in transmitted light with crosswise arranged papyrus strips (2x); (b) ancient pa­pyrus sheet (344 B.C.) with adhesive starch layer (500x)

Figure 4. DTA curves of recent papyrus sheets from Egypt and Sicily (sample weight: 1.75 mg; heating rate: 0.5 °C/min)

Figure 5. DTA curves of (a) pressed and (b) beaten papyrus sheets (heating rate: 0.5 °C/min)

Figure 6. DTA curves of dated ancient papyri (sample weight: 2.5 mg; heating rate: 0.5 °C/min)

which results in a lowering of the heat of combustion. The small endothermic peak developed at 140 °C (Figure 5b) is caused by the dehydration of calci­um oxalate monohydrate. This obser­vation agrees with the well-known fact that fast-growing plants such as sedge, reed, and papyrus contain oxalic acid. Calcium oxalate is then formed by re­action with calcium assimilated from the soil and incorporated into the cell walls. Larger amounts of calcium oxa­late may be generated during the beating process by reaction of residual oxalic acid in the cell walls with the calcium-containing water in the capil­laries of the plant. The additional exo­thermic DTA peak in the temperature range 320-390 °C is due to the decom­position of calcium oxalate into the carbonate, with evolution of carbon dioxide.

To determine how the lignin peak changes with age, we asked the Egyp­tian Museum in Berlin for dated sam­ples from 600 B.C. to 600 A.D. DTA curves of these samples are shown in Figure 6. These curves show that the lignin peak decreases slightly with in­creasing age of the sample.

The yellow-brown coloration, which is almost always present in ancient pa­pyrus materials, probably is caused by a higher degree of dimerization of the lignin. These colorations could be sim­ulated on fresh papyrus. Papyrus strips heated for 1 h from 100-220 °C showed increasing intensity of brown coloration. DTA curves of these sam­ples showed that the lignin peak de­creases with increasing temperature while the cellulose peak remains prac­tically unchanged. Papyrus that has been heated does not become as in­

tensely dark because the heating de­stroys part of the lignin, which is washed out and therefore not avail­able for dimerization during heating.

Mass Spectrometric Investigations Another useful method for our in­

vestigations was pyrolysis mass spec­trometry (MS). The amount of sample necessary for such studies is extremely small, 10-50 μξ. The sample is heated to 500 °C in the oven, which is con­nected to the mass spectrometer. The pyrolyzates are continuously di­rected toward the ionization source. This technique allows the integrat­ing registration of all volatile pyroly­zates generated in the complete pyrol­ysis procedure.

Typical mass spectra recorded dur­ing the pyrolysis of cotton cellulose, lignin, and the ancient papyrus West-car are shown in Figure 7. The spec­trum of cellulose indicates the pres­ence of levoglucosane (m/z 162) and its decomposition products (m/z 144, 126), furan (m/z 98), acetic acid (m/z 60), and ionized methanol (m/z 31). The spectrum of lignin shows the presence of coniferyl alco­hol, a lignin monomer (m/z 180), as well as other substituted lignin phe­nols.

To investigate the effect of age on cellulose structure we recorded mass spectra of pyrolysis products from cot­ton cellulose and papyri of various ages. Peaks with m/z 162 and 144 de­creased or disappeared with increasing age, indicating that levoglucosane, the monomeric building block of cellulose, undergoes single or multiple dehydra­tion with time. Eventually, it is trans­formed to levoglucosenone (m/z 126).

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Figure 7. Mass spec t ra of pyro lys is products f r o m co t ton , l ignin, and anc ien t papyrus

The spectrum from the papyrus West-car illustrates this dehydration.

TMA Studies The swelling behavior of papyri was

also investigated in relation to age by subjecting a number of papyri to dy­namic TMA. Figure 8a shows the TMA cell. The sample is placed between the vitreous silica platform and movable S1O2 rod and subjected to a variable load. After equilibration (3-5 min), water is added to the dish. Figure 8b shows the swelling behavior of a fresh and an ancient papyrus sample. First there is a sudden contraction due to the imbibition with water, followed by a parabolic swelling curve. Taking the fresh papyrus as a reference (100%), the ancient papyrus (578 A.D.) shows swelling on the order of 5-6%. Further experiments with ancient papyri from different periods showed that papyri

from about 1000 B.C. swell about 2-3% whereas papyri older than 1500 B.C. show no expansion at all (9).

D e c a y of P a p y r i

A serious problem encountered with historic papyri involves their state of preservation, since they are usually very fragile. The gradual browning of papyrus has been mentioned already. In addition, many papyri are also par­tially destroyed by fungi, which can be identified by electron microscopy. It is not possible to use DTA in such stud­ies since there is an overlapping of the peaks of cellulose and of the chi-tin, a celluloselike biopolymer that occurs typically in many fungi and is characterized by its high chemical re­sistance. Blue-green algae have also been found on some of the ancient papyri, in particular on the papyrus Ebers (2000 B.c.) (10).

Another source of severe damage to ancient papyri was the unintentional use of corrosive pigments. The green color (verdigris, basic copper acetate) was especially destructive, since it de­composes by gradually splitting off acetic acid, causing degradation of the papyrus (11). Many ancient papyri have been destroyed by this reaction; one example is the papyrus Book of Death, shown on p. 1221 A.

C o n c l u s i o n s

Our work included a number of dif­ferent techniques, all of which con­tribute to a better understanding and knowledge of the manufacture and composition of one of our first "pa­pers." Thermoanalytical method stud­ies like DTA, TG, TMA, and pyrolysis MS show that the proportions of the main constituents of papyrus—cellu­lose and lignin—vary with age, manu-

Figure 8. (a) TMA cel l and (b) TMA curves of papyrus

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factur ing process, and env i ronmenta l effects. Generally, cellulose is the more s table componen t . In all papyr i t he H2O con ten t remains r a the r cons tan t a t ~ 1 0 wt %. Papy r i t h a t have been bea t en show the typical T G ca lc ium-oxalate peak a t ~ 1 4 0 °C and a de­crease in the lignin con ten t in relat ion to t he cellulose. Th i s decrease of lignin is also found when papyr i are par t ia l ly des t royed by the effect of fungi.

F u r t h e r m o r e , t he s tudies show t h a t t he yel low-brown coloration of anc ien t papyr i is p robably due to the higher degree of polymerizat ion of the lignin cons t i tuen t s . Th i s effect can be accel­e ra ted by higher t empera tu re s . T h e browning effect may be inhibi ted to some ex ten t when the papyri are beat­en dur ing their manufac ture . Such t r e a t m e n t dest roys p a r t of t he lignin, which is washed out and no longer available for polymerizat ion.

Microscopic invest igat ions prove t h a t all the anc ien t pre-Chr is t ian pa­pyri up to 350 B.C. conta ined a layer of s ta rch . Younger papyr i , however, were manufac tu red wi thou t t he aid of a s ta rch binder .

Finally, invest igat ions on the swell­ing behavior of papyr i show t h a t th is p rope r ty decreases with increase in age of t h e papyri and is pract ical ly

zero for papyr i from per iods before 1500 B.C.

Acknowledgment W e t h a n k Will iam K. Simpson, Mu­

seum of Fine Arts , Boston, for t he sample of t he papyrus Reissner, D. Debes , K. Marx Universi ty, Leipzig, G.D.R., for samples and pho tographs of the papyrus Ebers , and the Bib-lotheca Bodmer iana , Cologny Geneva, Swi tzer land , for permiss ion to repro­duce the pho tog raph of the papyrus Book of Dea th . We also t h a n k J. Se t t -gast , d i rec tor of the Egypt ian Muse­um, Wes t Berl in, for the papyrus sam­ples men t ioned in Figures 2, 6, and 8 a n d H.-R. Schul ten , Fachhochschule Fresen ius , Wiesbaden , F.R.G., who carr ied ou t t he mass spec t rometr ic in­vest igat ions.

References

(1) Lucas, A. "Ancient Egyptian Materials and Industries," 3rd éd.; Arnold: Lon­don, 1959; p. 548.

(2) Pliny. "Natural History"; Loeb Classi­cal Library: London, 1952.

(,'i) Pliny. "Natural History," translation of 4th Volume by H. Rackham; Harvard University Press: Cambridge, Mass., 1960.

(4) Hepper, F. N.; Reynolds, T. "Papyrus and the Adhesive Properties of Rs Cell Sap in Relation to Paper-making," J.

Egypt. Archeol. 1967, 53, 156. (5) Ragab, H. "A New Theory Brought

Forward About the Adhesion of Papyrus Strips," 14th International Congress of Paper Historical, Manchester, 1978.

(6) Wiedemann, H. G.; Muller, V. G.; Bayer, G. "Old Egyptian Papyrus Inves­tigated by Thermogravimetrical Analy­sis"; In "Proceedings of the Vth ICTA Conference"; Kagaku Gijutsu-sha: Japan, 1977; pp. 373-75.

(7) Wiedemann, H. G. "Paper technology from Egyptian, Chinese, and Mayan cul­tures," National Bureau of Standards Special Publications 580; "Proceedings of the Workshop on the State-of-the-Art of Thermal Analysis"; NBS, Gaithers-burg, Md., May 21-22, 1979 (issued May 1980).

(8) Basile, C. "A Method of Making Papy­rus and Fixing and Preserving It by Means of a Chemical Treatment"; In "Conservation of Paintings and the Graphic Arts"; Lisbon Congress 1972; In­ternational Institute for Conservation of Historic and Artistic Work: London, 1972; p. 901.

(9) Wiedemann, H. G. "Application of Thermoanalytical Methods for Differen­tiation between Ancient Papyri"; In "Proceedings 4th Int. Conf. Surface and Colloid Chemistry"; Jerusalem, July 1981, 1981, p. 122.

(10) Ebers, G. Papyrus Ebers; Verlag von Wilhelm Engelmann: Leipzig, 1875.

(11) Banik, G. and Ponalho, I. "Some As­pects Concerning Degradation Phenome­na of Paper caused by Green Copper Containing Pigments"; Int. Council of Museums, 6th Annual Meeting, Ottawa, 1981.

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